The present invention relates generally to an apparatus and method for the formation of a fiber or continuous filament, and more particularly to the formation of a fiber which consist of two separate and different components.
It is well known to form synthetic fibers by extruding molten polymers through a large number of very small openings formed in a die.
It is also well known that such synthetic fibers can be formed of two polymer components having different characteristics and physical properties, such as so-called xe2x80x9csheath-corexe2x80x9d fibers that have one component (the core) centered within the other (the sheath). In forming these sheath-core fibers, it is very important that the core be centered within the sheath because if the core is offset from the center by even a slight amount, the quality and physical properties of the resulting fiber can be seriously flawed.
In forming these sheath-core fibers, it is common practice to provide a pre-die plate which is formed with a first plurality of openings extending therethrough and through which one of the components flow, and a second die plate having a second plurality of openings through which the second component flows as it becomes joined with the first component and is discharged through the bottom or discharge openings in the die plate in the aforesaid sheath-core configuration.
It will therefore be apparent that the alignment between the first and second plurality of openings in the pre-die plate and the die plate can be critical because if the first openings are slightly misaligned with respect to the second openings, the core component will not be centered with respect to the second component, and the resulting fiber may have the aforesaid disadvantages.
When it is recognized that both the pre-die plate and the die plate are formed with an inordinately large number of openings extending therethrough, all of which are very small, it will be quickly apparent that the tolerances involved are quite close. Therefore a slight misalignment between these small openings is always possible.
Moreover, this problem is greatly exacerbated by the fact that the fiber components must be maintained in their molten state during their flow through the two plates, which therefore may reach also very high temperatures (up to 350xc2x0 C.), still considering the different melting grades of the two components.
Since the plates are formed of steel, these elevated temperatures (and their inherent variations), cause the dimensions of the plates to change, either through expansion or contraction, and these changes can move one set of openings in one of the plates relative to the openings in the other plate, which can create a very undesirable misalignment of the two sets of openings.
Accordingly, there is a need in the art to provide a simple and reliable method and apparatus which will compensate for any misalignment between the openings in the two plates, and will insure that the core component will be centered with respect to the sheath component.
In accordance with the present invention, an apparatus is provided for making fibers or continuous filaments consisting of first and second components, such apparatus including a first plate having an inlet for receiving the first fiber component, and having a first plurality of openings through which the said first fiber component flows to an outlet end of the openings. A second plate is juxtaposed with said first plate and has a second plurality of openings therein which are generally axially aligned with the said first plurality of openings in said first plate, and the said second plate having a flow channel that permits the said second fiber component to flow to the second. openings and out through an outlet end of the said second openings.
A plurality of flexible hollow tube members are mounted to extend axially into the second plurality of openings with one end of each of the flexible tube members being located adjacent the outlet end of one of the first openings and with the other end of each of the flexible tube member being located adjacent the outlet end of the said second openings. The flexible tube members present a cross-sectional area less than the cross sectional area of the second openings, and they are sufficiently flexible to accommodate any misalignment between the said first and second openings without adversely affecting the flow of the first and second components.
In the preferred embodiment of the apparatus of the present invention, each of the flexible tube members has centering vanes located at the aforesaid other end thereof which extend outwardly and into engagement with the walls of the second openings, and these vanes are dimensioned to center such other end of the flexible tube member in the second opening, and to maintain such other end of each flexible tube member axially aligned with the second openings even if such one end of the flexible tube member is not axially aligned with the second opening.
Preferably, the flexible tube members are mounted in the first openings of the first plate at the outlet end thereof.
Also, in the preferred embodiment of the present invention, the second plate includes die openings adjacent the outlet end of the second openings and communicating therewith so that the second component flows from the second openings into the die opening, and the other end of each flexible tube member has a discharge opening directing the flow of the first fiber component into the die opening within the flow of the second fiber component to thereby form a sheath-core fiber or continuous filament.
The present invention also includes a method forming a fiber or a continuous filament from two fiber components comprising the steps of positioning a first upper plate having a plurality of first openings therein immediately adjacent a second lower plate having a plurality of second openings therein and a plurality of die openings in the bottom face thereof, with said first and second opening being generally axially aligned. The method includes the step of positioning a plurality of flexible hollow tube members so that one end of each flexible tube member is in communication with each of the first openings, and so that the flexible tube members extend into the second openings generally in axial alignment therewith, with each flexible tube member having a cross-sectional area less than the cross-sectional area of said second openings to form a flow channel therebetween. The same method includes the step of causing the flexible tube members to flex adjacent the upper ends thereof to accommodate any axial misalignment between said first and second openings.
The method also includes the steps of creating a first flow path for the first fiber component that extends through the first openings and through the interior of said flexible hollow tube members to be discharged from the flexible hollow tube members and through the die openings; and creating a second flow path for the second fiber component that extends through the second openings and around the exterior of the flexible tube members to be discharged from said second openings and through the die openings in a manner that surrounds the flow of the first fiber component through the die openings, to thereby form a sheath-core fiber or continuous filament.
In the preferred embodiment of the present invention, this method also includes the steps of disposing the lower ends of the flexible tube members at the bottom end of the second openings, and mechanically maintaining such lower end of the flexible tube members centered with respect to the second openings particularly maintaining the lower end of each said flexible tube members axially aligned with the second openings and the corresponding die openings, even if the upper end of the flexible tube members is not axially aligned with the second openings.